The use of ultrasound for determination of physical properties, texture, and microstructure is well known. Specifically, it is also well known that ultrasound velocity of a material is directly proportional to its density and porosity. However, in order to determine ultrasound velocity in materials (material velocity) or other properties, the conventional ultrasound mode involves either direct or indirect contact of a transducer to the test material. For example, in order to efficiently transmit ultrasound in the test material, the transducer is physically coupled to the material by liquid couplants, dry contact couplants, or by submerging the material in liquids, generally water. Conventional ultrasonic coupling modes cannot be effectively applied to materials such as consolidated particles (green ceramics, powder metals, pharmaceutical tablets and other like materials), porous, early stage formation of polymers, and other materials that are sensitive to liquid couplants or any contact. Therefore, in order to ultrasonically analyze these materials, it is necessary to develop a new ultrasound mode that is free from any contact with the test media. The current invention is based upon very high efficiency Non-Contact Ultrasound (NCU) transducers, such as the one described in U.S. Pat. No. 6,311,573, entitled “Ultrasonic Transducer for High Transduction in Gases and Method for Non-contact Transmission in Solids,” herein incorporated by reference in its entirety. This invention not only eliminates contact with the materials, but with careful analysis of ultrasonic signals in conjunction with appropriate electronic components, creates a functional mechanism for NCU velocity measurement, and thus its relationship with material density.
Kulkarni, et al. exhibit such relationships (“Ultrasonic Characterization of Green and Sintered Ceramics: I, Time Domain,” Am. Cer. Soc., Cer. Bull, Vol. 73, No. 6, 1994) by utilizing dry coupling transducers and Bhardwaj (“Non-Contact Ultrasonic Characterization of Ceramics and Composites,” Proceedings Am. Cer. Soc., V 89, 1998) and Carneim, et al. (“Non-Contact Ultrasonic Characterization of Green Bodies”, Cer. Bull., April 1999) by utilizing NCU method, all of the foregoing of which are hereby incorporated by reference in their entirety.
The primary objective of this invention is to determine the test material ultrasound velocity (as well as to relate it to its density) without any contact of transducers or coupling liquids with the material. According to this invention ultimately, the only coupling medium for ultrasound transmission in test material is a gas, such as air, either under ambient or under high pressure environment.